How can I discover the author of a blendfile?
You can't, This author field is only ever used in exporters. In the COLLADA export to be precise, where the COLLADA format can have an author tag, and I wanted it to be possible for users to have a configurable content for this, so I added the author field to user preferences.

Not everybody will have this set, either, so best not to rely on this for 'correct' user data.